1. Field of the Invention
This invention relates to a superconducting-normal-superconducting (SNS) Josephson junction and, more particularly, to a method for using ion implantation to create a normal layer in an SNS Josephson junction.
2. Discussions of the Related Art
Josephson junctions are used in a variety of high temperature superconductor (HTS) integrated circuits. A Josephson junction is superconducting device capable of switching signals from one circuit to another in as little as 6 ps. Thus, Josephson junctions rely on the ability of superconducting electrons to tunnel back and forth between a first and second superconducting layer. This tunneling behavior depends on many things, including the thickness and type of the normal layer material.
To fabricate an SNS junction, a thin film of HTS material is deposited on a substrate and then patterned using photolithography techniques to create a first superconductive layer (or base electrode). An insulating dielectric layer and a second superconducting layer (or counter electrode) are formed over the first superconducting layer, and then patterned to form individual SNS junctions. The thicker the dielectric (i.e., normal layer), the more difficult it is to achieve the preferred tunneling behavior. Thus, one of the primary impediments in preparing uniform, high-quality SNS Josephson junctions is the ability to precisely control the thickness and material type of the normal layer. For instance, it is often difficult to deposit uniformly thick normal layers because uneven coverage occurs especially in the early stages of film growth. Small surface features, such as outgrowth and pores, can also inhibit uniform coating of the normal layer. Non-uniformity in the normal layer thickness or composition can lead to a poor quality junction. (e.g., electrical shorts, non-uniform tunneling, etc.).
Therefore, a method for fabricating a SNS Josephson junction addressing the above-identified problems is desirable for use in a high temperature superconductive integrated circuits.